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Many experience people taught me about feedforward control was figure out on above loop arrangement picture. They simply explained feedforward means the sensor or transmitter was installed on the upstream of process and the control valve was installed on the downstream of process. I am worry that many experience people have been spreading this missunderstanding to many young professional in Indonesia particularly.

My Boss said no body perfect in instrumentation and control because this technology always change and change. For those who academically close their eyes about the changing of technology they would run behind, getting tired, and getting down.

Re-arrange the Missuderstanding

Continuous Process Control-Practical Guides for Measurement and Control (ISA), P.G. Friedman & T.P. Stoltenberg mentioned Feedforward control attempts to sense the disturbance and take compensating action before disturbance has an affect on variable controlled by a feedback loop. Harold L. Wade in Regulatory and Advanced Regulatory Control: System Development (ISA) mentioned that the objective of feedforward control is to drive the controlling device from a measurement of the disturbance that is affecting the process, rather than the process variable it self. My friend Nugroho Wibisono (ConocoPhillips) also clearly explained in id-instrumentation@yahoogroups.com mailing list that feedforward is a loop to compensate disturbances.

If we refer to above loop the PT is process variable, PIC is pressure control, and PCV is manipulated variable. That loop is main loop with purpose to control the process variable which is PT. PT is not a disturbance being measured. But the PT is controlled variable itself. What is the disturbance? It is not found on the above loop. So It is nothing to do with feedforward control if we want to refer to the paper or article of the ISA.

I am trying to understand feedforward control base on below loop diagram.